Burglar alarm systems



1968 R. A. PALLADINO 1 BURGLAR ALARM SYSTEMS 2 Sheets-Sheet 1 FiledMarch 4, 1966 INVENTOR ROBERT A. PALLADINO ATTORNEY POWER SOURCE R. A.PALLADINO BURGLAR ALARM SYSTEMS Oct. 29, 1968 2 Sheets-Sheet 2 FiledMarch 4, 1966 INVENTOR ROBERT A. PALLADINO ATTQRNEY CORRECT r 3;- Y

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United States Patent 3,408,642 BURGLAR ALARM SYSTEMS Robert A.Palladino, 34 Aspen Road, West Orange, NJ. 07052 Filed Mar. 4, 1966,Ser. No. 531,677 Claims. (Cl. 340276) This invention relates to burglaralarm systems, and especially to improvements in the type of systemwhich is controlled by a combination or permutation of numbers in anumerical sequence entered into the system, for instance by dialing amultiple-digit sequence, for the purpose of controlling the alarmsystem.

It is a principal object of the present invention to provide a system inwhich authorized personnel are provided with a number comprising aseries of digits which they can enter into the system by way of atelephone-type dial in order to either test the system, or to turn thesystem on, or to turn the system off, whereby no keys or othermechanical devices are necessary in order to control the system whileavoiding the setting off of needless alarms.

It is another important object of this invention to provide an improvedsystem in which authorized personnel can change the digits comprisingthe correct combination in a simple and quick manner so as to make iteasier to maintain full security, and inrwhich there is no limit to thenumber of digits which can be used in a correct combination, additionaldigits being provided at relatively small extra expense.

Another object of the invention is to provide an improved system whereinthe dial by which th correct combination of numbers is entered, whencontrolling the system, is located inside the guarded premises, and inwhich the system provides two time delays, one of which delays initialactivation of the alarm system long enough after dialing the combinationto permit authorized personnel to unlock the premises, enter, and dialthe correct combination to turn off the system before an alarm isactually sounded.

Another important object of the invention is to provide an improvedburglar alarm system in which the burglar sensing wiring around doorsand windows is provided with a certain value of ohmic resistance whichthe alarm system is adjusted to continuously measure, and wherein analarm will be set off if the value of this resistance is changed. Inthis way, unauthorized persons cannot gain access, by either clippingthe wiring or by short-circuiting it, without setting off the alarm. v

Still another object of the invention is to provide a system havingthree dial-controlled conditions: Off, Delay with System Checking, andOn. An authorized person departing the guarded premises will dial thecorrect combination to change the system from off to delay, and thisdelay period is adequate to permit the departing person time during thedelay period to observe system indicator means which check certainspecific conditions of the system, including continuity of the burglarsensing wires and the condition of a stand-by emergency battery. Afterthis delay period has terminated, the system then automatically moves toon condition where it remains until it is either tripped into action oruntil the correct combination 'is redialed to change the system to offcondition.

Another object of the invention is to provide a system in which thealarm, once set off, can be disabled only by dialing the correctcombination again into the system. At any time when a person dials awrong digit into the system, the alarm is immediately set off.

A further object of the invention is to provide a system in whichbattery stand-by power is provided so that the system will not bedefeated by a general power failure at the guarded premises. The systemmay be arranged if desired so that a power failure will set off thealarm, or alternatively so that a general power failure will merelychange the system over to battery operation.

A further object of the invention is to provide an improved remote alarmsystem to be installed at a local police station, this alarm systemproviding different alarm which respectively signify the differencebetween ,unbalancing of the resistance measuring bridge, as by tamperingwith the burglar sensing wiring, and power failure at the guardedpremises. Cutting or short-circuiting of the wires to the police stationwill also result in the latter type of alarm being set off.

Other objects and advantages of the present invention will becomeapparent during the following discussion of the drawings, wherein:

FIGS. 1A and 1B when placed side-by-side together form a schematicillustration of a system according to the present invention.

General description Referring now to the drawings in detail, the presentsystem comprises a burglar alarm which is operated by a dial resemblinga telephone dial, by way of which persons can dial numbers into thesystem. If the person dials the correct number (three digits in thepresently illustrated embodiment), the alarm system is advanced into abrief delay period, from which it then automaically moves into anoperative or on condition. On the other hand, if the person dials anyincorrect digit when the system is in on condition, the alarm isimmediately set off and can be turned off only by dialing the correctnumber sequence into the system.

In order to accomplish th above purpose, the system shown in theschematic diagram includes a dial 15 which operates a first steppingrelay 20 to step the contacts located above the winding on the schematicdiagram through a certain number of positions depending upon the digitentered via the dial 15. This dialing sequence sequentially grounds oneof a group of wires connected to the terminals of a second steppingrelay 30, these terminals being in a vertical column generally indicatedby the reference numeral 31. This stepping relay is of a type which goesthrough its four sequential positions and then begins the sequenceagain. The first three positions correspond with the three digits to beentered by way of the dial 15, and the fourth digit serves a switchingpurpose to be hereinafter explained.

The outputs from the row of stepper terminals 31 are connected to theterminals of three IO-pcsition-two-circuit selector switches appearingin columns above the reference character 40, and including the switch 41which corresponds with the first digit to be dialed, the switch 44 whichcorresponds with the second switch to be dialed and the switch 47 whichcorresponds with the third digit to be dialed. Each of the switchesincludes two sections. One of these sections in each switch is of thetype in which all contacts are shorted except the selected one, forinstance as illustrated by the switch sections 42, 45, and 48. The otherswitch section is of the type in which all of the contacts are openexcept the one which is selected, and these sections are labeled 43, 46,and 49. The wires which represent wrong numbers entered via the dial arerespectively selected by the switch sections 42, 45, and 48, and thewires which represent the correct digits in each dialing sequence areselected by the switch sections 43, 46, and 49. The three selectorswitches 41, 44, and 47 are controlled by separate shafts (not shown)and are located in an inconspicuous or lock-protected place since theycontrol what combination of digits must be dialed for the purpose ofcontrolling the present alarm system.

Whenever a correct digit is dialed, a relay 50 is actuated via theappropriate switch section 43, 46, or 4'9, but whenever an incorrectnumber is dialed, a different relay labeled 60 is energized through anappropriate switch section 42, 45, or 48. Whenever the relay 60 isenergized the alarm is sounded immediately. The appropriate contacts forthe relays 50 and 60 are shown to the right of the relay windings.

The alarm system itself includes, for example, two different bells, andalso includes time-delay circuitry which provides a brief delay intervalbefore the system sounds an alarm in order to permit authorizedpersonnel, to have time to set the alarm and leave the premises, or toenter and dial a number to turn off the system. The delay and alarmcircuits are generally shown to the right in FIG. 1B.

The following detailed discussion supplements the above generaldescription of the layout of the system:

Dialing system The dial 15 and the first stepper 20 cooperate tofunction in the manner of a conventional telephone dialing system havingten selectible digits for each dial rotation. The stepper 20 has twocircuit sections including the lower section 21 and its wiper 22, andthe upper section 23 and its wiper 24. The stepper has two solenoidactuators, including a winding 25 operative to advance the wipers 22 and24 to the next sequential position, and including a reset winding 26,which when energized resets all the wipers to their rest positions inwhich they appear on the present drawing. The stepper 20 is advancedeverytime the switch 16 is closed as the telephone dial returns throughone of its digital positions, whereby the switch 16 pulses the winding25 with a series of pulses whose number is determined by the number towhich the dial is manually turned. When the dial 15 reaches its restposition, the switch 17 is mechanically closed, this switch being openWhenever the dial is in any other position.

It will therefore be observed that whenever the dial 15 has stepped thestepper 20 out of its rest position, a circuit is completed through thewire 27 and the bank of contacts 21 to the wire 29 from the power sourceP so as to place positive voltage upon one end of each of the relaywindings 50 and 60. If the other end of either of these relay windingsis grounded through stepper section 23 by way of the terminals 31 andthe selector switches 40, then that relay, 50 or 60, will becomeenergized.

It is the function of the second stepper 30 via its contacts 31 to jointhe stepping bank 23 of the dial-operated first stepper 20 with eitherthe selector switch 41, 44 or 47 depending upon which digit in thesequence of threedigit dialing is being dialed. There are ten wipers tothe left of the contacts 31 and these wipers are respectively connectedto positions 1 through of stepper bank 23. When the wipers are allconnected to the lowermost of the four positions in each group ofcontacts 31, all of the ten positions from stepper bank 23 are thenconnected to ten positions of the selector switch 41 corresponding withthe first operation of the dial. In the presentschematic, it will benoted that the switch 41 is set on position 8 so that if a person dials8 in the first digit, when the dial returns to rest position closingswitch 17, a ground connection will be made through switch 17 and toterminal 8 in stepper bank 23 and to the switch section 43 whichhas beenmanually set to the number 8 position. A ground connection will therebybe made to the wire 59 and to the upper end of relay winding 50 toenergize the correct-number relay 50.

When this correct first digit has been dialed, the relay 30 steps all 10wipers to the next-higher contacts in the groups of contacts 31, andthese contacts are connected to the selector switch 44 correspondingwith a second operation of the dial. When the dial returns to restposition the second time and the switch 17 closes, if the operator hasdial 5, the wiper 24 will be on contact 5 of stepper bank 23, therebyproviding a grounded circuit through selector switch section 46 to thewire 59 to again energize the correct-number relay 50. The secondclosing of the relay 50 advances the stepper 30 to place the Wipers onthe third-contacts-up in the stepper contacts 31, thereby connecting the10 positions of the stepper bank 23 to the 10 positions of the selectorswitch 47. If the person dials 1 for the third digit, the relay 50 isclosed again, thereby advancing the second stepper 30 to the fourthposition in the bank of contacts 31, which contacts are all unused inthe bank 31 although the fourth contacts are used in the bank 32 locateddirectly beneath the winding of the stepper 30. The bank of contacts 32then carries out certain functions which will be described hereinafter,culminating in resetting the second stepper 30 to the first (lowermost)position.

On the other hand, whenever a person dials a wrong digit, that is, anumber different from 8 in the first digit, 5 in the second digit, or 1in the third digit, a wire is grounded through the bank 23 to one of theselector switch sections 42, 45, or 48, thereby energizing the wire 69,closing the relay 60 and immediately setting off the alarm. Means isprovided by which the alarm continues to operate until it is manuallyreset by a person dialing the correct sequence of digits, 8-5-1, as willpresently be described. Thus, the dialing of just one wrong digit in anysequence immediately sets off the alarm.

Although the illustrated positions of the selector switch 40 show thatthe correct number to be dialed is 8-51, this number can be changed inthe first digit by moving the switch 41, in the second digit by movingthe switch 44, or in the third digit by moving the switch 47. In thismanner any desired three-digit combination can be selected.

Correct num'ber dialed Whenever a correct digit has been entered in thedial 15 in the manner described above, the wire 59 becomes grounded,thereby energizing the correct-number relay 50 and moving the contacts51 and 52 to their lower positions. When the contact 51 is in the lowerposition, it breaks the circuit through the dial switch 17 to thestepper bank 23 until the relay 50 becomes deenergized again, at whichtime the contact 51 again closes the circuit from the switch 17 to theband 23 to energize the next digit. Moreover, the contact 51 placesground current upon the wire 39 through the switch 17 to pulse thesecond stepper 30 to its next sequential position. When relay 50 closesit advances stepper 30 and returns stepper 20 to its rest position. Whenstepper 20 is returned, it breaks the circuit through wire 29, thusreleasing relay 50 to drop open in preparation for the next dialingsequence. Whenever the relay 50 is closed, the contact 52 is lowered,thereby connecting ground current to the wire 28 and energizing thereset winding 26 to return the first stepper 20 to its rest position inpreparation for the dialing of the next sequential position.

When all three selected digits have been correctly dialed, the closingof the contacts 51 for the third time pulses the second stepper 30 intoits fourth position in which the wires 33 and 34 are both grounded atcontacts 32. The stepper 30 remains in the fourth position pending thefollowing sequence of events.

There is a third sequential stepper which controls the on-otf conditionof the alarm system and operates four sets of contacts 81 sequentiallythrough three positions, the cycle being continuous and progressingthrough three contact positions as the winding 80 is progressivelygrounded at its upper end. Assuming that the contacts 81 are in theiroff position as shown in the drawing, when the contacts 32 move into thefourth position and ground the wire 34, the upper end of the winding 80is grounded, thereby moving the contacts 81 into their intermediateposition, labeled delay. In this position of the contacts 81, the wiper82 connects a voltmeter V temporarily across a battery B, which servesthe purpose of sustaining the alarm in spite of a power failure, andthis voltmeter provides a momentary showing of the condition of thebattery. Also in this delay position of the stepper 80 the wipers 83 and84 connect the wires 86 and 87 in series between a light bulb 88 and theplus 12 volt supply so that if the light bulb lights, it provides anindication that the burgler sensing wiring W which is attached to thepremise around its doors and windows is continuous. This wiring of thebuilding is connected to terminals 87a and 86a, and comprises one oranother well known type of resistance tape, for instance having aresistance of about 50 ohms per foot. There is a normally-closed switchcontact 64 connected in series between the wire 86 and the contact 8611when the system is alert, and the reason for this contact will bediscussed hereinafter.

When the third stepper 80 was energized via the wire 34, it also closedcontacts 89 and connected grounded wire 33 to wire 38 and wire 39,thereby energizing the winding of the second stepper 30 to step it backto its first position (the one shown in the drawing).

The contact 85 is grounded, and when the stepper 30 is in theintermediate or delay position the contact 85 energizes a time delayrelay 90 having a single normallyopen contact 91. The interval of delaycan be selected to suit the desires of the owner, but a delay ofapproximately 90 seconds is desirable to give the operator time in thedelay condition of the system to observe that the lamp 88 is lighted toconfirm continuity of the sensing wiring W, that the voltage measured bythe voltmeter V across the alarm battery B is adequate, and then toleave the premises after locking the door and before the 90 second delayis over. When the delay ends, the relay 90 closes the contacts 91, againgrounding the coil of the third stepper 80 and stepping the contacts 81into the third or on position. The stepper 80 then remains in thisposition until someone enters the correct sequence of digits into thedial 15.

As mentioned above, when the time delay relay 90 closes, it advances thethird stepper 80 to move the contacts 81 to the third or on position,thereby deenergizing the time delay relay 90, taking the voltmeter offof the battery B, and moving the contacts 83- and 84- to their uppermostpositions in which the wires 86 and 87 coming from the resistive burglarwiring W are connected across the open leg L of the Wheatstone bridge92. The resistors 93, 94, and 95 are selected to operate with the ohmicvalue of the burglar wiring W in order to balance the Wheatstone bridge92. The resistance 95 is made adjustable to effect exact balance of thebridge so that no voltage appears across its terminals a and b when theterminals 0 and d are connected respectively between the 12 volt supplyand ground through the wiper 85.

The circuit remains quiescent in the on position of the stepper 80 solong as the bridge 92 remains balanced, and so long as nobody dials awrong number into the dial 15. However, if someone either short-circuitsthe burglar wiring W connected to the terminals 86a and 87a, oralternatively breaks this wiring, the Wheatstone bridge 92 becomesunbalanced, and current flowing through the wires 92a and 92b closes thesensitive relay 96, thereby moving the contacts 97 and 98 into theirlowered positions. The making of contact between the wires 92a and 97akeeps the relay 96 energized because it short-circuits part of thebridge 92 and thereby maintains it in unbalanced condition even thoughthe burglar wiring may be restored. The closing of the contact 98 placesground potential upon the wire 99, and therefore energizes the timedelay relay 100, which relay waits a certain number of seconds and thencloses, setting off the alarm. The delay, of for instance 30 seconds,interposed by the relay prevents the sounding of the alarm long enoughto make it possible for authorized personnel to open a door, enter thebuilding, and take steps to prevent the alarm from going off byredialing the correct sequence of digits, in the manner to be presentlydescribed. If the unbalance of the bridge is not counteracted by anauthorized person who knows how to do it within the 30 second time-delayassumed for the relay 100, at the end of this delay the relay 100 willoperate to open its normally closed contact 101, which results insetting off the alarm.

Alarm The alarm system is shown in the upper right-hand corner of FIG.1B and includes the battery B, a bell connected so that it can besounded by the battery despite a commercial power failure which disablesthe power source P, and further includes a second bell labeled 70 whichis connected on one side to the power source P through a wire 72 so thatit can be powered independently of the battery B. The alarm system alsoincludes two other relays 73 and 111 whose windings are connected inseries between ground at one end through a fuse 109, and the plus 12volt supply line through the normally-closed contacts 101 of the timedelay relay 100. As long as the contacts 101 are closed (the relay 100deenergized) the relay windings 73 and 111 are both energized so thatthe contacts 74, 75, 76, and 112 are in their lower positions asillustrated in dashed lines, whereby the wire 71 is held disconnectedfrom ground so that the alarm 70 is disabled, and also so that thecontact 112 is open and the bell 110 is disconnected from the battery B.

However, when the 30 second time delay has ended and the relay 100closes due to unbalance of the bridge 92, the contact 101 opens, therebydeenergizing windings 73 and 111 and permitting the contacts 74, 75, 76and 112 to return to their normal positions illustrated in solid lines,in which positions the bell 70 is connected to ground via the wire 71 sothat it is caused to continuously ring, and so that the bell 110 isconnected across the battery B via the contact 112, thereby also causingit to continuously ring. As pointed out above, the relay contact 97throws a permanent unbalance on the bridge 92 so that the relays 96 and100 both remain energized to main tain the alarm continuously operative.

The only way to stop the alarm is to dial the correct sequence ofnumbers into the system again by actuating the dial 15. If a wrongnumber is dialed, nothing happens and the alarm continues to sound, butif the right digits are dialed, each correctly dialed digit advances thesecond stepper 30 in accordance with the sequence set forth above. Thefirst and second numbers which are dialed merely advance the secondstepper 30 to receive another digit, but the third correct numberadvances the stepper 30 to its fourth position, thereby grounding wire34 at bank 32 and advancing the third stepper 80 from the on positionback to the OE position and thus removing power from the bridge 92 andthe relays 96 and 100 so that the contacts 101 resume their normallyclosed condition. When the relays 73 and 111 are reenergized, they closeto break the contacts 74 and 112 which were causing the bells to ring.

The present system includes one additional alarm feature provided by thewires 115 and 116, which may comprise telephone lines leading to a localpolice station. At the far ends of the lines, are located two oppositelypoled diodes 117 and 118, and each of these diodes is connected inseries with the winding of a relay 120 and- 121 respectively. It will beseen that in the on condition of the system (relays 73 and 111 energizedand contacts 75 and 76 down) the line 115 is positive with respect toline 116 and the relay 120 will be energized to close 7 the contacts 122and disable the alarm 124. The contacts 123 will remain open so that thealarm 125 is also disabled. Recalling that the alarm is set off wheneverthe relays 73 and 111 become deenergized, it will be noted thatdeenergizing of relay 73 moves the contacts 75 and 76 to their uppermostpositions so that the wire 116 becomes positive with respect to the wire115. Therefore, the relay 120 will open and the relay 121 will close andonly the alarm 125 will be connected across the battery A if unbalanceof the bridge caused the alarm situation. But, if this change was causedby a general failure of power at the source P, then only alarm 124 willring since neither relay 120 nor 121 will be energized.

Wrong number dialed As stated above, whenever a wrong number is dialedin any digit, the relay 60 is immediately actuated thereby moving thefour wipers 61, 62, 63, and 64 from the upper (rest) positions shown inthe drawing to their lower positions; When this occurs, the lowermostcontact 61 grounds the wire 71 setting off the alarm device 70, forinstance illustrated as a bell, which continues to ring so long as therelay 60 is energized. When the relay contact 62 moves downwardly, itbreaks the circuit between the normally closed switch 17 at the dial andthe selector bank 23 so that even if another digit is dialed it will nothave any effect on the system once the alarm has gone off. When thewiper 63 is moved to the down position, it grounds the wire 28, therebyenergizing the reset winding 26 of the first stepper 20, and returningboth of its banks to the rest position shown in the drawing. Inasmuch asthe first stepper has been returned to rest position, the ground currentpath is removed from the wire 69, and the relay 60 drops open, therebyreturning the wipers 61, 62, 63, and 64 to their up positions as shownin the drawing. However, when the contact 64 of the relay 60 was movedto the down position as a result of dialing a wrong number, it broke thecircuit to the external burglar wiring W, thereby unbalancing the bridge92 just as though the building were being burglarized, and when thebridge 92 was unbalanced, it closed the relay 96, and applied acontinuous short-circuit across the bridge via the wire 97 to maintainthe bridge unbalanced. Therefore, at the end of 30 seconds, the timedelay relay 100 closes and deenergizes relays 73 and 111, causingcontinuous sounding of the alarms 70 and 110, as well as alarm 125,until a person equipped with the correct number dials this number intothe system by way of the dial 15, thereby resetting the system to offcondition.

The structures of the stepping relays 20, 30 and 80 have been simplifiedby omitting the intermittent interrupter contacts which are part ofstandard stepping relays such as Universal Relay Corporation Model R-977or Type 26. The capacitors across the windings reduce inductive kicksand line noises.

The present invention is not to be limited to the exact illustrativeembodiment, for obviously changes may be made therein within the scopeof the following claims.

I claim:

1. An alarm system for protecting a guarded area having intrusionsensing wiring connected in series, comprising:

(a) a source of power;

(b) alarm means;

(c) first relay means connected in circuit between the source and thealarm means and holding the circuit open when the first relay means isenergized;

(d) measuring means coupled to said sensing wiring and sensitive tochanges in the resistance of the latter;

(e) second relay means connected to the measuring means to be actuatedby the latter in response to a change in said resistance, and includingnormallyclosed contacts connected to energize the first relay means fromsaid power source unless the, second r'elay means is energized; (f)digital switching means connected to control the on-otf condition of thesystem by controlling said digital means including means forpreselecting a plural-digit numerical sequence and renderingth'eswitching means responsive to the selected sequence to alternatelychange its condition between ona;n'd

Off; I

(g) digital entry means connected to said switching means to enter asequence of digits thereinto; and V (h) means connected to saidswitching means for cou; pling thealarm means directly to the powersource whenever a nonselected digit is entered.-

2. In a system as set forth in claim 1, said digitalswitching and entrymeans comprising: f I,

(a) first stepping switch means having first contacts for each numeralwhich, can be entered in a digit, and being sequentially controlled bythe entry means to connect one of said contacts to the power'sourcep (b)a manual selector switch corresponding with each digit in said sequence,and each switch having a wrong-number bank of contacts and having acorrect-number bank of contacts, one contact in each bank correspondingwith each numeral which "can be entered in a digit;

(c) second stepping-switch means having contacts representing eachnumeralwhich can be entered and these contacts being connected betweencorresponding contacts of the first stepping switch meansand therespective contacts'of all of said manual switch banks; I H

(d) means for advancing the second stepping switch means to connect thefirst contacts to a different manual selector switch each time a digitis entered;

(e) third stepping switch means having a continuous sequence ofpositions including contacts for establishing said on and offconditions; and

(f) means controlled by said second stepping switc means after the lastdigit in the numerical sequence is entered for advancing the position ofthe third stepping switch means.

3. In a system as set forth in claim 2,

(a) a third relay means connected to the correct-number banks of theselector switches and energized when a correct digit is entered toadvance the second stepping switch means; V

(b) fourth relay means connected to the wrong-number banks of theselector switches and energized when a wrong digit is entered to couplethe alarm to the power source;

(c) means responsive to energizing of either the third or fourth relaymeans to return the first stepping switch means to a rest" position; and

(d) means connected between the measuring means and the fourth relaymeans and responsive to energizing of the latter to simulate a change inthe resistance being measured.

4. In a system as set forth in claim 1, said measuring 60 meanscomprising:

(a) a plural-leg bridge circuit connected across said power source andincluding said sensing wiring in one leg, and balanced to provideno'output' across two of its junctions unless said resistance changes;

(b) fifth relay means connected to said junctions and actuated when thebridge is unbalanced, and including contacts connected to maintainbridge-unbalance after the relay is actuated.

70 5. In a system as set forth in claim 4,

(a) said second relay means comprising a delayedaction relay having afirst time delay, and connected to be energized by said fifth relaymeans whenthe latter is actuated, the second relay means opening saidnormally-closed contacts after said delay.

6. In a system as set forth in claim 1, said digital switching meanshaving contacts arranged to be switched in sequential positionsincluding an off position, a delay position, and an on position; and thesystem further including:

(a) means connected with the contacts in the delay position for checkingthe continuity of the sensing wiring;

(b) means connected with the contacts in the on position for energizingthe measuring means from the power source; and

(c) second time delay means connected to the contacts in the delayposition and energized thereby to advance the digital switching means tothe on position after the period of delay.

7. In a system as set forth in claim 1, said power source comprisingcommercial power lines, and said alarm means comprising:

(-a) auxiliary battery means;

(b) two alarm indicating means; and

(c) said first relay means comprising two relays having contactsrespectively connecting one indicating means with said power lines andconnecting the other indicating means with said battery means, and saidrelay means when energized holding the contacts open, and both relaysbeing energized from said power lines.

8. In a system as set forth in claim 7, said power source delivering DC.power having a constant polarity, and said first relay means includingtwo contact members connected to said DC. power;

(a) a remote alarm station joined by wires to said first relay means sothat there is a first polarity on the wires when the first relay meansis energized, and a reverse polarity on said wires when the relay meansis deenergized;

(b) battery means at the remote station;

(c) two alarm sounding means at the remote station and each connected onone side to the battery means;

(d) third and fourth relay means at the station each having actuatingwindings and having contacts respectively interposed between onesounding means and the other side of the battery means such that the 10third relay means breaks these contacts when energized, and the fourthrelay breaks these contacts when deenergized; and

(e) oppositely-poled diode means respectively connecting the windings ofthe relay means so that the third relay is energized only by said onepolarity and so that the fourth relay is energized only by said reversepolarity.

9. In a system as set forth in claim 1,

(a) said measuring means comprising a Wheatstone bridge having saidsensing wiring connecting one of its legs, the bridge being connected toreceive power from said digital switching means which is connectedacross two opposite bridge terminals, and the other two bridge terminalsbeing connected to said second relay means; and

(b) the bridge being normally balanced so that no power flows to thesecond relay means unless the resistance of the sensing wires issubstantially changed.

10. In a system as set forth in claim 1, said digital switching meansincluding means for interposing time delays in its response While beingcontrolled to change between on and off conditions whenever :a selectedsequence of digits is entered into the system.

References Cited UNITED STATES PATENTS 791,961 6/1905 Weatherby 3402851,290,644 1/1919 lNelson 340276 1,923,968 8/1933 Chase 340276 X2,606,237 8/ 1952 Chase 340274 X 2,843,843 7/1958 Davis 340276 2,855,58810/1958 Allen 340276 2,964,733 12/1960 Raju 340276 X 3,024,452 3/ 1962Leonard 340274 3,029,420 4/ 1962 Bagno et a1. 340-276 X 3,128,414 4/1964Miehle 340164 X JOHN W. CALDWELL, Primary Examiner.

D. L. TRAFTON, Assistant Examiner.

1. AN ALARM SYSTEM FOR PROTECTING A GUARDED AREA HAVING INTRUSIONSENSING WIRING CONNECTED IN SERIES, COMPRISING: (A) A SOURCE OF POWER;(B) ALARM MEANS; (C) FIRST RELAY MEANS CONNECTED IN CIRCUIT BETWEEN THESOURCE AND THE ALARM MEANS AND HOLDING THE CIRCUIT OPEN WHEN THE FIRSTRELAY MEANS IS ENERGIZED; (D) MEASURING MEANS COUPLED OT SAID SENSINGWIRING AND SENSITIVE TO CHANGES IN THE RESISTANCE OF THE LATTER; (E)SECOND RELAY MEANS CONNECTED TO THE MEASURING MEANS TO BE ACTUATED BYTHE LATTER IN RESPONSE TO A CHANGE IN SAID RESISTANCE, AND INCLUDINGNORMALLYCLOSED CONTACTS CONNECTED TO ENERGIZE THE FIRST RELAY MEANS FROMSAID POWER SOURCE UNLESS THE SECOND RELAY MEANS IS ENERGIZED; (F)DIGITAL SWITCHING MEANS CONNECTED TO CONTROL THE "ON"-"OFF" CONDITION OFTHE SYSTEM BY CONTROLLING SAID DIGITAL MEANS INCLUDING MEANS FORPRESELECTING A PLURAL-DIGIT NUMERICAL SEQUENCE AND RENDERING THESWITCHING MEANS RESPONSIVE TO THE SELECTED SEQUENCE TO ALTERNATELYCHANGE ITS CONDITION BETWEEN "ON" AND "OFF"; (G) DIGITAL ENTRY MEANSCONNECTED TO SAID SWITCHING MEANS TO ENTER A SEQUENCE OF DIGITSTHEREINTO; AND